Light Emitting Diode (LED) light strings have become quite popular recently for holiday decorating. They are much more energy efficient than incandescent lighting that has been around for many years. Since both the LED and the more conventional incandescent mini-light operate at very low voltage—usually between 2.0 to 3.5 volts—they are wired in electrical series connection with approximately 35 to 50 lights in a light string. As with incandescent lighting, when an LED bulb burns out, is loose or missing from the socket, the entire series light string goes out. To prevent this, bypass shunts can be wired across each LED to continue current through the light string in the event of such a failure.
Various other attempts have heretofore been made to provide various types of shunts in parallel with each series light of a series wired light string, whereby the string will continue to be illuminated whenever a light has burned out, or otherwise provide for an open circuit condition. For example, in Applicant's U.S. Pat. No. 6,580,182, entitled SERIES CONNECTED LIGHT STRING WITH FILAMENT SHUNTING, the disclosure of which is incorporated by reference herein, there is disclosed and claimed therein various novel embodiments which very effectively solve the prior art failures in various new and improved ways. For example, there is disclosed therein a series string of lights powered AC voltage, each light having a silicon type voltage regulating shunting device connected thereacross which has a predetermined voltage regulating value which is greater than the voltage normally applied to said lights, and which said shunt becomes fully conductive only when the peak voltage applied thereacross exceeds its said predetermined voltage switching value, which occurs whenever a light in the string either becomes inoperable for any reason whatsoever, even by being removed or falling from its respective socket, and which circuit arrangement provides for the continued flow of rated current through all of the remaining lights in the string, together with substantially unchanged illumination in light output from any of those remaining operative in the string even though a substantial number of total lights in the string are simultaneously inoperative for any combinations of the various reasons heretofore stated. There is disclosed therein various type of shunting devices performing the above desired end result, including back-to-back Zener, or so-called “avalanche” diodes, non-avalanche bilateral silicon switches, and conventional Zener diodes, one-half of which are electrically connected in one current flow direction and the remaining one-half being electrically connected in the opposite current flow direction.
In U.S. Pat. No. 6,084,357, a series of rectifier diodes are connected in an array across light sockets to continue current flow in the event of a failure. This patent teaches the use of two arrays connected in parallel in opposite electrical directions to simulate counter-connected Zener diodes. U.S. Pat. No. 6,580,182 teaches the use of two counter-connected (back-to-back) Zener diodes across each lamp socket. Other patents teach the use of a single Zener diode as a shunt in an AC rectified DC circuit.
Applicant's U.S. Pat. Nos. 6,084,357; 6,580,182 & 6,765,313 are incorporated here in their entirety. The circuits disclosed and claimed in those patents offer a vastly superior series connected light string with shunting which avoids much of the disadvantages of the prior art circuits noted above. U.S. Pat. No. 8,415,887, by the present inventor and owned by the present assignee, provides such a circuit for an LED light string. It would be desirable to provide an LED with an internal bypass transistor for use in the circuit of U.S. Pat. No. 8,415,887, to simplify the circuit and minimize cost.
It is therefore a principal object of the present invention to provide a simple and inexpensive, and yet highly effective, internal silicon type shunt, or bypass, for each of a plurality of series connected LEDs in a light string.